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Control 3 case fans from 1 motherboard connection?

Last response: in Components
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January 27, 2010 9:06:28 PM

I am about to get a new CoolerMaster HAF 922 case (http://www.newegg.com/Product/Product.aspx?Item=N82E168...) which has 3 case fans with 3-pin connectors. The motherboard has only one 3-pin connector though (http://www.newegg.com/Product/Product.aspx?Item=N82E168...). Ideally I would like to connect the fans to the motherboard so that the fan speed can be adjusted automatically (quieter when the computer is idle).

Now, as a solution, I've noticed that you can get a fan power splitter cable (http://www.newegg.com/Product/Product.aspx?Item=N82E168...) and with 2 of these, I could connect all fans to the motherboard. But would it be OK in terms of current/voltage? Would it confuse the mobo?

Or, is there a better solution for controlling the fans from the mobo?
a c 134 ) Power supply
a c 207 V Motherboard
January 27, 2010 9:14:47 PM

Enthusiast boards have more fan connectors and higher amp ratings. The Asus R2E for example has 8 fan headers, each rated for 2 amps each. With the 922's 200mm fans, I don't think I'd want all that power draw on one header...remember, it's not just the steady power draw "when running" but "inrush current" that you have to consider when fans are started. With a 2 amp header rating on a hi end board w/ well regulated power, I'd be comfy with 2 or maybe 3 120mm fans rated at 0.33 amps on a good quality board (2:1) safety margin). 200mm fans would make me nervous.

If I were you'd I'd get one of these:

http://www.newegg.com/Product/Product.aspx?Item=N82E168...

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January 27, 2010 9:18:47 PM

OK, I see. So to be safe, I should get a board with enough fan connectors. I didn't know that that's differentiating factor for the enthusiast boards :-)
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January 28, 2010 7:11:54 AM

The board you linked to has 2x 3-pin fan connectors and 2x 4-pin connectors. One of the 4-pins is for the CPU fan, but you can connect a 3-pin fan header to either one as well. So, there's plenty of connections to hook up 3 case fans and a CPU fan right to the mobo.

Unless you linked to the wrong board and yours really only has one fan header, then you need to get an add-on fan controller.
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January 28, 2010 11:34:39 AM

The motherboard is indeed ASUS P7P55D-E. I haven't bought it yet so I can take a look but the user manual states:

1 x CPU fan connector (4-pin)
2 x Chassis fan connectors (1 x 3-pin, 1 x 4-pin)
1 x Power fan connector (3-pin)

The slot for the CPU fan is taken, but you are right, I could put the 3 fans in the remaining 3 connectors. Does this mean that:
- 4-pin connectors are compatible with 3-pin fans? Can the mobo still control the rotation?
- it is OK to put a case fan in the power fan connector? Doesn't this mean that the mobo would take the wrong temperature reading?


The manual also says that the power fan connector does not support the Fan Xpert feature, so that one would probably run at full speed all the time.
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January 28, 2010 12:02:38 PM

In terms of current:
- the manual states that it supports 1A for each fan header
- the 200 mm fans are .160~.280 A

So together they would be .560 A, barely out of the the 2:1 safety margin suggested by JackNaylorPE.
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a c 248 ) Power supply
a b V Motherboard
January 28, 2010 1:03:35 PM

For reasons already stated by others it is not a good idea to power multiple fans from one fan connector on the motherboard.

There is another inexpensive option available. You can definitely connect the extra case fans directly to your power supply. In fact you can safely daisy chain the fans and connect them to one 4 pin molex connector. No problem. All you need is a 3 or 4 pin fan connector to 4 pin molex adapter. Here is a link to one example:

http://www.newegg.com/Product/Product.aspx?Item=N82E168...

Of course the downside is that you cannot control the fan speed if a fan is connected directly to the power supply.

I understand that you want a quieter pc when your pc is idle. Have you considered getting a quiet pc case and building a quiet system? Have you looked at passive cooling? Have you explored the use of quiet fans? I am a Coolermaster fan and I have the HAF 932. The 932 and 922 were not designed as quiet cases. Instead they were designed for excellent ventilation, airflow, and cooling.


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January 28, 2010 1:22:47 PM

Right, but then the mobo would not be able to control their rotation if I connect them directly to the power supply. This build is for a regular desktop, not a high-end gaming machine and I would expect that most of the time the fans would not need to run at full speed. The resulting quietness is a big bonus for me.

I am surprised that for this build I have the go through such hoops to connect the fans: 3-pin vs 4-pin, only 2 connectors for chasis fans, a.s.o.

Two years ago in my previous build with an ASUS P5K-E (which was in the same $150 range), it had 3 x 3-pin connectors for the chasis fans and I didn't even think about fan/mobo issues.

Why did they come up with the new 4-pin connectors (sorry for my ignorance)? Are they fully compatible with 3-pin fans (including speed control)? As far as I can see, most cases still come with 3-pin connectors.

Thank you.
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January 28, 2010 1:28:34 PM

Hi JohnnyLucky,

Yes, I am totally open regarding the choice of case. I kind of looked at Antec P183 and Sonata, but those also have loads of fans and I was again worried about mobo connections. For my PC, one front intake for the hard disk and one back exhaust should probably be enough. Any recommendation of such a case which also looks sort of elegant? My one requirement is to not look like an alien :-)
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Best solution

a b ) Power supply
a b V Motherboard
January 28, 2010 2:05:47 PM

bcalmac said:
The motherboard is indeed ASUS P7P55D-E. I haven't bought it yet so I can take a look but the user manual states:

1 x CPU fan connector (4-pin)
2 x Chassis fan connectors (1 x 3-pin, 1 x 4-pin)
1 x Power fan connector (3-pin)

The slot for the CPU fan is taken, but you are right, I could put the 3 fans in the remaining 3 connectors. Does this mean that:
- 4-pin connectors are compatible with 3-pin fans? Can the mobo still control the rotation?
- it is OK to put a case fan in the power fan connector? Doesn't this mean that the mobo would take the wrong temperature reading?


The manual also says that the power fan connector does not support the Fan Xpert feature, so that one would probably run at full speed all the time.


Almost right. In reality you CAN use both Chassis Fan connectors for case fans, but not the others. The CPU fan connector MUST be used for the CPU fan or nothing else. The Power Fan connector is ONLY for use with what looks like a fan connector coming directly out of the PSU. In fact, this one does NOT provide power or speed control to anything. It merely allows the mobo to monitor the speed of the PSU fan via the signal sent TO the mobo. That is why the manual says this port does not support the Fan Xpert feature.

Normally at least one of the mobo's CHA_FAN connectors has its output power to the fan controlled by BIOS. And yes, you CAN use any 3-pin fan on any 3-pin OR 4-pin mobo output connector. The only detail not clear to me is whether BOTH of the CHA_FAN connectors have their fan speed outputs controlled together by the same mobo sensor and control loop, or whether only one of the two is controlled, and one is a fixed output speed. The manual implies that BOTH output pinouts are controlled.

The manual also says that the output capacity of each pinout is 1 amp max at 12 VDC. So if your fans are, say, 300 mA each and we allow for more than that as inrush current for starting up, I suggest you could connect two fans to one pinout safely, but not three. So you'd connect two case fans in parallel to one CHA_FAN pinout, and the third to the other. You'd connect your CPU cooler fan to the CPU_FAN pinout, and the PSU's apparent "fan connector" (only if there is one) to the mobo PWR_FAN pinout.

To connect the two case fans in parallel you could just mod the two fans' wiring yourself, or use the 2-from-1 adapter you showed. HOWEVER, I have a real problem with that adapter! It needs to be modified slightly. A 3-pin fan connection uses the black lead for Ground, the red one for variable-voltage DC power to the fan (that's how speed is controlled), and the yellow to feed a fan speed pulse signal (2 pulses per revolution) back to the mobo to monitor. That speed monitoring function just counts the pulses on the line and displays the fan speed for you. It MAY (depends on mobo) actually take some action IF that fan speed drops to zero - many current mobos DO take quick action if the CPU FAN speed (but not others) drops to zero. The problem with connecting two fans together in parallel by simply splicing the matching color leads together - which is exactly what that adapter does - is that this feeds TWO pulse signals back to the mobo, leading to possible confusion. I would recommend you use the adapter - makes it easy to connect two fans together - BUT just cut ONE of the yellow wires and tape up the ends. This will leave those two fans powered together from one mobo pinout, and only ONE of the fans' speed signals being fed back for monitoring. The mobo will never know or display anything about the second fan's speed, so it will be up to you to check on occasion that it is still working. For the third fan, plugged by itself into the second mobo pinout, there is no problem at all - the mobo is set up to recognize and monitor this port's speed signal separately.
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January 28, 2010 2:17:48 PM

Thanks for the detailed answer. I'll probably look for a case with only 2 fans, which should be enough for a regular desktop.
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a b ) Power supply
a b V Motherboard
January 28, 2010 2:25:23 PM

I can supply PART of the answer on 4-pin connectors for fans. First, recognize that the physical connectors are plastic moldings made in such a way that they only go together one way, and so that a 3-pin female connector can fit on a 4-pin male output connector. The wiring is arranged so that the first 3 pins are the same for either male pinout - Ground on one end, + 12VDC (variable) next, and speed pulse signal (third). The fourth pin only is used if the fan's female connector contains a fourth socket to match the fourth pin. To see how the pins are used, look at the manual for that mobo on page 2-37. The 3-pin arrangement is shown for the PWR_FAN and CHA_FAN2 pinouts. The 4-pin arrangement is shown for the CPU_FAN pinout.

A 3-pin system controls fan speed by changing the DC voltage supplied to the fan on the red wire (+12 VDC or less). A 4-pin fan's motor design is different. Its power is NOT a DC voltage, but a 25 kHz square wave signal with the "Duty cycle" or "% on" varied according to the required fan speed. The pinout male connector puts this output on the fourth pin, labeled CPU FAN PWM, where "PWM" stands for "Pulse Width Modulated". The fan does not actually need the DC voltage line directly. So any mobo BIOS controller can be designed to generate both types of power output to the 4-pin mobo pinout, and the fan connected to it will use the signal appropriate to that fan.

What I find a little confusing in the manual is that it shows the CHA_FAN1 mobo's pinout as having on its fourth pin a +5 VDC fixed signal, rather than the PWM power signal. Maybe this is a simple misprint in the manual, I don't know.
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January 28, 2010 2:30:35 PM

Best answer selected by bcalmac.
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